This invention relates in general to capillary devices and in particular to an injection system useful in capillary electrophoresis (CE).
High performance CE, which includes capillary zone electrophoresis and electrokinetic chromatography, has a high separation efficiency and the ability to work with extremely small samples. Thus, this method is very useful for the separation of complex mixtures commonly encountered in the biomedical field.
With capillary zone electrophoresis (CZE), an electric field is applied between the two ends of a capillary tube into which an electrolyte is introduced. The electric field causes the electrolyte to flow through the tube. A sample containing a mixture of solutes is injected at the inlet of the capillary. Some solutes will have higher electrokinetic mobilities than other solutes so that the solutes form zones in the capillary tube during the flow of the electrolyte through the capillary.
The analytical scheme of a typical CE system includes sample injection, separation on the capillary column, and detection. Sample introduction in CE has been accomplished in a number of ways. These include manual sample injection, rotary-type, electromigration, and hydrodynamic flow devices. See Schwartz et al., J. Chromatogr., 480 (1989) 129-139.
However, these injection methods all are far from ideal. For example, it is necessary to interrupt the applied voltage during the injection procedure for all these methods. Thus, there is always a time in the separation procedure when the high voltage is not applied. This time lag may cause problems in the reproducibility of elution time of a solute. Moreover, these previous methods are not applicable for all types of capillaries, and in particular, fail with larger cross-sectional area capillaries. For example, the use of a rectangular capillary has several advantages in CE, but is difficult to use with gravity injection. Finally, previous sample injection techniques often require the physical disturbance of the analytical column. For instance, with gravity injection it is necessary to alter the position of the capillary during injection and with electromigration one end of the column is positioned into direct contact with the sample.
There is a critical need for a sample injection device and method for use in capillary electrophoresis that can be applied to circular or rectangular capillaries, that can be used safely by the operator, and that have a minimum disturbance on the CE separation. Furthermore, the device and method should afford good control over the amount of sample injected and should be easily adaptable for use with an autosampler or auto-injection system. Finally, there is a need for a continuous device and method that permit sample introduction without the need to disengage the applied electric field or to disturb the physical environment of the capillary column.